Casting Aluminum - small amounts to thermally connect parts in a host

[Blindasabat]

I have been thinking about modding my Vistalight Nightstick Code headlights to LED for several years. The Helmet mount is the best I've seen and they use 35mm MR11 size halogen bulbs. I think I can drop in a flat AL heat sink if I can connect the sink to the cast body of the light, but I suspect the body is not AL. I'd like to either duplicate the entire body with an added integral one piece cast AL sink OR fill the gaps between my hand ground sink to the metal body with molten AL. I figure I can plaster or sand pack one side at a time to cast in (connect to the existing body with molten AL) the sink I have already fabbed. This may require pictures to fully illustrate what I want to do. This is a view of the heat sink placed where it needs to be with clearance cut away for the ribs, mount nut, and switch:

So my question is:
Does anybody have any suggestions, tips, and/or experience casting AL?

I plan to get a small graphite crucible. Can I then melt a few grams of AL with a torch to the crucible or do I need a more extensive setup?

Thanks all.

 

[Blindasabat]

Two more views of the host

 

[KC2IXE]

Get the Dave Gingery books!

Also, look up "Hobby Foundry"

All sorts of interesting info out there. The HUGE issue is making the molds, and setting up the sand. For a part like that, you're looking at lose cores etc

Another option would be lost wax casting - that's another whole fun area

 

[Norm]

How about making a heatsink similar to the one shown, make it a firm fit and then glue it in place with thermal epoxy (Arctic Alumina).
Norm

 

[ICUDoc]

Doesn't aluminium burn in air when you heat it up to just above melting point? Looks like a fascinating task ahead. I need something similar for the inside of an M6 head.

 

[65535]

Aluminum is fine, magnesium, and titanium are commonly casted metals that must be done in inert gasses or they will pretty much blow up when poured.

Casting aluminum in and of itself is fairly easy, its relatively low melting point slow oxidation and good flow make it easily castable.

BUT setting up a foundry and mold are time consuming at best.

 

[russthetoolman]

I got an education from attending a steam and scale model show in my local area. The older guys there know so much about doing this and they were willing to have me come to their meetings after the show at their homes to do this with them.
Russ

 

[Blindasabat]

Thanks for the info guys. Ideally, I'd like to have a solid Aluminum structure from sink to body of the HL which is why I thought of casting. I could cram some rolled up aluminum foil in to take up some space. I though of cutting the HL housing apart and inserting a computer heat sink, but can't cut the odd shape straight enough to keep it lined up. I could drill some holes and thread in some aluminum screws from the outside through the housing an dinto the sink to connect it to the outside.
Solder has much higher thermal resistance, so I want to avoid that for a high performance light (something K2 at over 1.5 Amp or XP-G at 1.2A for an hour plus ride).
I will have to consider some of the alternative ideas if casting turns out to be too difficult, but my wife actually suggested I put an ad out on the Alchemy area of Etsy.com to see if any local hobbyists could do it.
The model making guys are a good start too, I'll have to see if there is a show like that around here.

I tried to cut that sink with tight clearance to the housing, but it was a long frustrating grinding job that ended up with too much clearance. There was always one spot too big, then all of a sudden it was all too small. Getting that to fit tightly and at the correct depth in the housing for the LED to focus well is not a task I'd wish on anyone.

Thanks guys!

 

[Fred S]

Consider lost foam casting, not too difficult to do at home. Fill your host with foam, pop the foam out and carve in whatever details you want. Cover the foam with plaster of paris (drown the foam in a bucket of the plaster). Melt the foam out with acetone and pour aluminum in the hole. If you want to get really fancy, you can put in runners and gates for better casting quality. Only thing to watch out for is casting shrinkage, it could be a fair amount for Al.

 

[Blindasabat]

I would need stiff strong foam right? Foam like this:
http://www.hobbyengineering.com/H1270.html
Or would a can of that expanding stuff (Great Stuff) work?

Then I make a model of the part I want to cast & cover that in plaster... I didn't think plaster would hold molten aluminum... Now to get a torch to melt by.

 

[Fred S]

Great stuff should be fine, the only real requirement is that it dissolves in acetone or some other solvent. I do know that any mold you use has to be nice and dry to prevent steam explosions. Have to bake the mold for several hours @4-500 deg. If you are worried about the mold failing, you can mix in some silica sand to give it some more heat resistance. It sounds like this is a one time thing, so it shouldnt be a big deal.

 

[Lyndon]

It doesn't have to be. My first try at melting aluminum took about 5 minutes setup: half filled a terracotta flower pot with BBQ charcoal, light it off, and then placed a soup can half full of aluminum scrap on the red hot coals. Air blast from below through the pot's drain hole with a $20 vacuum cleaner that had an outlet port and I was done. Full melt in about 15 minutes, IIRC.

Subsequent work was more involved, but you can get started cheap and easy.

BUT setting up a foundry and mold are time consuming at best.